<!doctype html>
<html><head>
<title>Border clipping</title>
<style>
.div1 { width: 50px; height: 50px;
      border: 10px solid black; 
      border-radius: 20px;
      position: absolute;
      background: black;
      left: 50px;
      top: 50px;
      background-clip: padding-box;
}

</style>
</head>
<body>
  <div class="div1"></div>
</body></html>
